1. Field of the Invention
The present invention relates to a wafer processing method for dividing a wafer along a plurality of crossing division lines, the division lines being formed on the front side of the wafer to thereby define a plurality of separate regions where a plurality of devices are formed.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines are formed on the front side of a substantially disk-shaped semiconductor wafer to thereby define a plurality of separate regions, and a plurality of devices, such as ICs and LSIs, are formed in the respective separate regions. The semiconductor wafer is cut along the division lines to thereby divide these separate regions where the devices are formed from each other, thus producing a plurality of individual device chips.
Cutting of such a semiconductor wafer along the division lines is usually performed by using a cutting apparatus called dicing saw. This cutting apparatus includes a chuck table for holding a workpiece such as a semiconductor wafer and an optical device wafer, cutting means for cutting the workpiece held on the chuck table, and moving means for relatively moving the chuck table and the cutting means. The cutting means includes a spindle unit having a spindle, a cutting blade mounted on the spindle, and a motor for rotationally driving the spindle. The cutting blade is composed of a disk-shaped base and an annular cutting edge mounted on one side surface of the base along the outer circumference thereof. The cutting edge is an electroformed diamond blade formed by bonding diamond abrasive grains having a grain size of about 3 μm, for example. The cutting edge has a thickness of about 20 μm, for example.
Since the cutting edge of the cutting blade has a thickness of about 20 μm as mentioned above, each division line for separating the devices must have a width of about 50 μm. Accordingly, the ratio of the area of the division lines to the area of the wafer is large to cause a reduction in productivity.
As another method of dividing a wafer such as a semiconductor wafer, a laser processing method called internal processing has also been put to practical use in recent years. This laser processing method uses a pulsed laser beam having a transmission wavelength to the wafer, wherein the pulsed laser beam is applied to the wafer in the condition where the focal point of the pulsed laser beam is set inside the wafer in a subject area to be divided. That is, the wafer dividing method using this laser processing method called internal processing includes the steps of applying a pulsed laser beam having a transmission wavelength to the wafer from one side of the wafer in the condition where the focal point of the pulsed laser beam is set inside the wafer, thereby continuously forming a modified layer inside the wafer along each division line, and next applying an external force to the wafer along each division line where the modified layer is formed to be reduced in strength, thereby breaking the wafer along each division line (see Japanese Patent Laid-open No. 2004-160493, for example).
As a method of applying an external force to the wafer along each division line where the modified layer is formed, thereby dividing the wafer into the individual device chips, there is disclosed in Japanese Patent Laid-open No. 2005-223282 a technique of attaching the wafer to a dicing tape supported to an annular frame and expanding the dicing tape to thereby apply a tensile force to the wafer, thereby dividing the wafer into the individual device chips along each division line where the modified layer is formed to be reduced in strength.
As another method of applying an external force to the wafer to thereby divide the wafer into the individual device chips, there is disclosed in Japanese Patent Laid-open No. 2013-165229 a technique of attaching a protective tape to the front side of the wafer in which the modified layer is continuously formed along each division line, holding the wafer through the protective tape on a chuck table, and grinding the back side of the wafer as supplying grinding water to thereby reduce the thickness of the wafer to a predetermined thickness and also divide the wafer into the individual device chips along each division line.